This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
What Is Spinosad?
A biological pesticide, spinosad is based on the bacterium Saccharopolyspora spinosa, which was discovered in 1982 in an old Caribbean rum still. It was soon found that these bacteria produce a substance that works as a neurotoxin in many (but not all) insects. Susceptible insect species that are exposed to spinosad become excited to the point of exhaustion, stop eating immediately, and die within two days.
Which Pests Does Spinosad Control?
Spinosad controls all types of caterpillars, and also has good impact on Colorado potato beetle larvae and blister beetles. Spinosad works best on pests that consume a lot of leaf tissue. There also are several fire ant baits based on spinosad, as well as a hair rinse for head lice.
How to Use Spinosad
In the vegetable garden, apply spinosad to dry leaves as soon as a target pest becomes evident. To a limited extent, spinosad is taken up by plant leaves, so one application often lasts for 10 days or more. Shake spinosad products well before using. Thoroughly wet both sides of leaves as well as places where insects may be hiding. Spinosad breaks down in sunlight, so late-day applications will better expose insects to the toxins. If honeybees are expected to visit the plants, exclude them with an old sheet or piece of row cover for 24 hours after applying spinosad.
Because spinosad is more persistent than Bt, do not apply it to leafy greens or vegetables that will be harvested within one week.
How to Store Spinosad
Mix only as much concentrate as you will need. If not used within a few days, dispose of unused solution by spraying it on grass-covered soil, far from drainage ditches or water supplies. Store spinosad products in their original containers on a high shelf, out of the reach of children and pets, in a dark place where temperatures will not go below 40 degrees Fahrenheit. Under good storage conditions, spinosad products last about three years.
More information on spinosad is available from Cornell University.